LONDON — As Europe’s first Mars probe remained stubbornly silent, British scientists on Monday announced a “last resort” plan to switch off the missing Beagle 2’s computer system for an overhaul.

Beagle 2 has not been heard from since it separated from the mother ship in mid-December, despite contact efforts by the European Space Agency’s orbiter Mars Express, NASA’s Mars Odyssey orbiter and British and U.S. radio telescopes.

The British-built lander was due to put down on the Red Planet on Christmas Day.

Colin Pillinger, lead scientist on the Beagle 2 program, said Mars Express passed over the probe’s landing site twice over the weekend, but nothing was heard.

Pillinger said his team would ask NASA to send a command from its Mars Odyssey orbiter on Tuesday to tell Beagle 2 to switch off its own computer and reload its software.

“We are now working on the basis that this is a corrupt system and the only way we might resurrect it is to send such a command and completely reload the software, if it’s still alive,” Pillinger said at a news conference in London.

“Of course, that is a very dangerous command to send, because if the thing is AWOL, or even if it’s there, it may never respond to it, so it’s pretty much a last resort,” he added.

If Odyssey fails, Pillinger said that Mars Express may also attempt to do the same thing on Feb. 2 or 3.

Pillinger said that his team would press on with the search for the missing probe, despite the bleak outlook.

“It would be incredibly useful to us to know how far in its mission it got because we are ... dedicated to trying to re-fly Beagle 2 in one way, shape for form,” he said.

Mars Express has had a more successful mission. Scientists at the European Space Agency said last week that Mars Express had found the
most direct evidence
yet of water in the form of ice on Mars, detecting molecules vaporizing from the Red Planet’s south pole.

Scientists have long believed the planet’s poles contain frozen water.

NASA scientists, meanwhile, worked to resolve their own problems with its Spirit rover that last week cut off what had been a steady flow of pictures and scientific data.

But American scientists are hopeful of pinpointing the problem and say Spirit could resume normal operations in two to three weeks. They also are celebrating the arrival of pictures over the weekend from Spirit’s identical twin, Opportunity, which was sent to the other side of the Red Planet.